I bought a used 600mm Sigma lens this morning for $135, and thought I'd compare it with my 100-400mm L + 1.4X TC. First, I took several shots and found that in the dark windy rainy weather that a 1/1000 sec image took a very high ISO setting on my 5D MK III, such that the image was noisy. So, I mounted the lens on a monopod, held my breath, and set the shutter speed to 1/320. My tripod was in the studio, and I did not want to brave the weather to go out and get it.

Then, I used the same setup with my 100-400 + TC. I could immediately see the difference thru the viewfinder, but went ahead and took the image for a first shot at comparing them.

To be fair, $135 versus almost $2000 worth of lens is a bit extreme, but I wanted to see the difference. I may have to get out that tripod after all, because there was a lot of difference, and some of it was movement.

Here is my first try, with images cropped and sharpened in Lightroom.

Sigma 600mm

Canon 100-400L + 1.4X MK II TC

To be fair, if you were printing the images at 8 X 10, I doubt that most people would see the difference, they look pretty good at a small size.

This afternoon, the wind and rain let up so I pulled out my heavy tripod and kirk ball head and put it at the same point that I took the handheld images. Its about 70 feet away. I had also disassembled the lens and blew out the dust that had accumulated over the years.

This time I focused on the flower using liveview at 10X, 1/500 sec and ISO 1600 with my 5D MK III. I had tried ISP 250 and 1/200 sec, but it wasn't as good.

I had to use NR, which did reduce the sharpness, so I added some sharpening back, quite a lot in fact.

I had forgot about how difficult using a lens like this one is. Even with a stable tripod, and heavy duty head, there was a lot of vibration when at 10X in liveview, so I damped it out by holding my arm over the tripod mount area of the lens.Its slightly better, and for the price ($135 used), its a bargain, but it does need a lot of care, and this dull and cloudy day required high ISO, so its a sunny day lens. I managed to avoid severe out of focus highlights, but there are always some. I might put some in on purpose, just in case someone likes dounuts.Full image:

I know you can't use an SX50 because of problems with your hands, but I and others get very sharp images and excellent IS with one at an effective fov of 1200mm, and that is a real bargain. The good thing about your experiment is that it shows us the drawbacks of mirror lenses. The Sigma does have a very bad reputation, and the Tamron has the best reviews.

After thinking about the poor light, I put on my 580 EX II with better beamer to focus the light out there 70 ft away, and used a manual exposure of 1/200 sec at ISO 200. Even this had a little too much in the way of highlights, but the exposure was pretty close.

Then I added vibrance, clarity, and a lot of NR. Adding that much NR is almost like adding noise, but I left it that way.

I think that a person on a tight budget could get by, its just a matter of spending the time and being ultra careful. Ordinary print sizes will be fine, and internet photos will be great.

Wow, the Canon made the bee mysteriously appear! I better go spray mine with insect repellant!

Seriously, I've toyed with a mirror lens and do appreciate what you've put up here. Seems on a bright day if what you are striving for is web images and not large prints, there could some use for these lenses.

Here is the last for the day, its getting dim outside, but I shot my crabapple tree with backlight coming thru the branches to see if the out of focus highlights were obvious. The wind has started up, so a high shutter speed and the ISO was up to 6400 which required a lot of NR.In this situation, I did not see any horrible highlights, so I'll wait for a sunny day, weather is supposed to clear up tomorrow.

I know you can't use an SX50 because of problems with your hands, but I and others get very sharp images and excellent IS with one at an effective fov of 1200mm, and that is a real bargain. The good thing about your experiment is that it shows us the drawbacks of mirror lenses. The Sigma does have a very bad reputation, and the Tamron has the best reviews.

I'm waiting for the SX60 in hopes that it has a touch screen. The SX50 is the real deal for those who don't have the issues I have. It could, of course be improved, but that applies to everything.

Wow, the Canon made the bee mysteriously appear! I better go spray mine with insect repellant!

Seriously, I've toyed with a mirror lens and do appreciate what you've put up here. Seems on a bright day if what you are striving for is web images and not large prints, there could some use for these lenses.

I bought it because it was cheap, and something I could play with. I bought a used Nikon 500mm about this time last year for $80 and adapted it to canon, and saw similar results before I sold it. You can see the doughnuts in the background.